The instant invention relates to the field of optical telecommunications, and more particularly to optical couplers for use in optical telecommunication systems.
An optical coupler is a device that transfers light signals from a plurality of input fibres to a plurality of output fibres. The simplest optical coupler is a four port 2xc3x972 coupler that operates in either a cross or a parallel state.
One example of a conventional 2xc3x972 cross optical coupler uses a pair of adjacent lenses to couple light from a first pair of input ports on one side of the device to a second pair of output ports on an opposite side of the device. The distance between the input ports is the same as the distance between the output ports.
However, in many optical systems the spacing between the input ports and the output ports is not the same. For example, the use of optical components such as twin isolators, polarization beam splitters, circulators, etc. typically results in different core to core distances between pairs of ports through which it is desirable couple. In these instances, mis-alignment results in significant coupling losses.
Prior art coupling devices have attempted to reduce coupling losses by either matching the core to core separation of input and output ports by physically moving them, or alternatively, by compensating for the lateral displacement loss. For example, with respect to the latter the use of thermally expanded cores has been found to make the lateral displacement loss less sensitive and to provide improved optical coupling. However, most of the proposed systems are unnecessarily costly and in many instances inconvenient, if at all feasible.
In fact, there remains a need for an efficient and economical optical coupler that minimizes coupling losses in four or more port systems where the spacing between adjacent pairs of ports is non-uniform.
It is an object of the instant invention to provide a method and device for efficiently providing optical coupling between a plurality of input ports and a plurality of output ports, where the spacing between the input ports is not the same as the spacing between the output ports.
It is a further object of the instant invention to overcome coupling losses normally associated in coupling systems where the spacing between the input ports is not the same as the spacing between the output ports.
The instant invention provides an optical coupling device and method wherein the spacing between two lenses is varied in a non-unitary configuration for improving optical coupling between two input ports and two output ports having different centre-to-centre distances.
In accordance with the invention, there is provided an optical coupling device comprising:
a first plurality of ports including a first port and a second port having a fixed distance d1 therebetween;
a second plurality of ports including a third port and a fourth port having a fixed distance d2 therebetween optically coupled to the first plurality of ports; and,
a first lens and a second lens having a non-unitary configuration disposed between the first and second plurality of ports for guiding a first non-collimated beam of light from the first port to the fourth port and a second non-collimated beam of light from the second port to the third port, the first and second lenses having a predetermined distance d3 therebetween selected in dependence upon the fixed distances d1 and d2 for ensuring that at least one of the first and second non-collimated beams of light emerges from the second lens at an angle to an optical axis thereof, wherein d1xe2x89xa0d2. 
In accordance with the invention, there is provided an optical coupling device comprising:
a first pair of ports having a fixed distance d1 therebetween for launching two non-collimated beams of light therein;
a second pair of ports having a fixed distance d2 therebetween optically coupled to the first pair of ports for receiving the two non-collimated beams of light; and,
a first lens and a second lens in a non-unitary arrangement disposed between the first and second pair of ports for directing the two non-collimated beams of light to the second pair of ports at an angle relative to each other, the first and second lenses having a fixed distance d3 therebetween selected in dependence upon the fixed distances d1 and d2, wherein d1xe2x89xa0d2. 
In accordance with the invention, there is further provided a method of optically coupling light from a first plurality of ports including a first port and a second port having a fixed distance d1 therebetween to a second other plurality of ports including a third port and a fourth port having a fixed distance d2 therebetween, comprising the steps of:
launching a first non-collimated beam of light from the first port towards a first lens having an optical axis;
allowing the first non-collimated beam of light to pass through the first lens and propagate along an optical path traversing the optical axis towards a second lens disposed a distance d3 from the first lens and having a common optical axis therewith;
allowing the first non-collimated beam of light to pass through the second lens and propagate towards the fourth port at an angle to the common optical axis; and,
receiving the first non-collimated beam of light at the fourth port.